1. Technical Field
Embodiments described in the present application relate to stimulating tools and methods of using the same in downhole stimulation applications, and more particularly to methods for controlling pressure pulses to enhance stimulation of a subterranean formation.
2. Background Art
There are several techniques for stimulating subterranean formations. The most commonly used technique is “hydraulic fracturing,” in which a stimulation liquid (with an acid or proppants) is injected into a well under high pressure to fracture the formations. Alternatively, subterranean formations may be fractured by detonation of an explosive charge in the wellbore which fractures the formation by shattering the rock.
Another technique of well fracturing involves the use of a device incorporating a gas generating charge or propellant, which is typically lowered into a well on a wireline and ignited to generate a substantial quantity of gaseous combustion product at a pressure sufficient to break down the formation adjacent the perforations. This type of fracturing technique differs from explosive fracturing in a number of ways: (1) this type of fracturing is caused by high pressure gaseous combustion products moving through and splitting the formation rather than shock wave fracturing; and (2) the process is one of combustion rather than explosion. Solid propellant fracturing generates high pressure gases at a rate that creates fractures differently from high explosives or hydraulic fracturing.
Typically, gas generation stimulation tools include a propellant charge, generally in a perforated carrier, of a length that is easily handled. The propellants in these tools are generally ignited by an electrical signal transmitted through an insulated wireline to an assembly which contains a faster burning material which is more easily ignited.
After a fracture has been created, it is desirable that the fracture extend as deeply as possible in order to reach the producing region. In order to extend a fracture, there should be a source of energy applying pressure to the fluid driven by the initial detonation into the fracture. Therefore, solid propellants are typically selected for the production of pressures on the order of those required for propagating a fracture.
While these techniques have been useful in well stimulation, there exists a continuing need for stimulation techniques that can control the burn rate of a propellant and/or the peak pressures generated therefrom, in order to achieve a predetermined degree of stimulation.